1. Field of the Invention
Embodiments of the present invention generally relate to methods of cleaning scale and deposits and altering the surface and shape of the inside diameter of tubulars.
2. Description of the Related Art
Hydrocarbon wells typically begin by drilling a borehole from the earth's surface to a selected depth in order to intersect a formation. Steel casing lines the borehole formed in the earth during the drilling process. This creates an annular area between the casing and the borehole that is filled with cement to further support and form the wellbore. Thereafter, the borehole is drilled to a greater depth using a smaller diameter drill than the diameter of the surface casing. A liner may be suspended adjacent the lower end of the previously suspended and cemented casing. Production operations often require lining the borehole with a filtration medium. Examples of common filtration media include slotted pipe or tube, slotted screens or membranes, and sand-filled screens. In general, the diameter, location, and function of the tubular that is placed in the well bore determines whether it is known as casing, liner, or tubing. However, the general term tubular or tubing encompasses all of the applications.
After completing various operations during the completion of the wellbore, ledges and debris are often left on the inside diameter of the tubular. Excess cement sometimes hardens on the inside of the tubulars after cementing of the liner or casing in the wellbore. Certain downhole milling operations leave metal pieces on the inside of tubulars from either equipment remnants or burrs on the tubular itself. For example, drilling out a packer in order to remove it from the tubular may not fully eliminate all of the metal that comprised the packer. Also, milling a window in the casing to run a horizontal bore causes metal burrs on the inside of the casing around the window.
Well tubulars often become plugged or coated during production from corrosion products, sediments, and hydrocarbon deposits such as paraffin. At elevated temperatures underground paraffin is a liquid and flows easily; however, the petroleum and paraffin cools off as the petroleum travels up the well bore toward the surface. At some point the temperature drops low enough to allow the paraffin to solidify on the tubulars in the well bore. Paraffin deposits primarily present a problem for sub-sea tubulars. Other scum and deposits on the inside of tubulars consist of silicates, sulphates, sulphides, carbonates, calcium, and organic growth. Soft deposits such as clay and sand from the formations can enter the bore at locations where the casing or liner has been perforated for production. Highly deviated and horizontal bores are particularly susceptible to collecting debris.
Debris that collects on the inside surface of the tubular that defines the bore can obstruct passage through the bore of tubing, equipment, and tools used in various exploration and production operations. Even if the tool can pass through the bore, debris often causes wear and damage to the tubing, equipment, and tools that pass through it. Sustaining production rates requires periodic cleaning since deposits and solidified paraffin on the inside of production tubulars slows down production of oil from the well.
Pressure changes in the wellbore, swelling of surrounding formations, earth movements, and formation changes deform downhole tubulars. Therefore, a cross section of downhole tubulars becomes more irregular and non-round over time. Exposure to erosion and corrosion add to the roughness and inconsistent roundness of the inside surface of the tubulars. Even initially, the inside surface of a tubular is typically rough and inconsistently round. Many tools used in downhole operations require a smooth round surface in order to properly operate or make a sealing engagement with the tubular. In addition, a polished bore receptacle that allows for a non-leaking engagement between two tubulars requires a smooth, clean, and substantially round surface. Placing a seal within a polished bore receptacle insures a fluid tight seal between the tool or tubular seated within the polished bore receptacle.
In order to create a polished bore receptacle, the roughness of the tubular's inside diameter must be smoothed, and the inside diameter of the tubular must be reformed into a more uniformly round surface. Since burnishing alters a tubular's surface characteristics, burnishing the inside diameter of the tubular can establish a polished bore receptacle. Therefore, the burnished inside diameter creates a smooth and substantially round surface.
Current operations to clean the inside of tubulars include circulating treating and cleanout fluids such as water, oil, acid, corrosion inhibitors, hot oil, nitrogen, and foam in the tubular. However, physical dislodging of the debris on the tubular walls is sometimes required. Fixed diameter reaming members, scrappers, shoes on the end of tubulars, and circulating cleanout fluids do not allow the ability to clean, alter the surface finish, and/or round various sizes of tubulars during one downhole operation. Additionally, these devices when used downhole for cleaning tubulars require costly and time consuming separate trips downhole to perform multiple operations such as cutting of the tubular or pressure testing within the tubular.
Therefore, there exists a need for an improved method of physically removing debris from the inside diameter of a tubular. There exists a further need for an improved method of burnishing the inside diameter of a tubular, thereby altering and rounding its surface characteristics.